QOL improvements and bugfixes.

GENERAL:

A replay code is provided after every online match played. It is possible to give this code to someone to watch a replay of that match.
Units have a killing counter.
Some amount of forest near players' starting points is now guaranteed.
It is required to set a movement target when creating a Goliath. The target can be changed later.

BUG FIXES:

Gate construction sometimes fails, but two adjacent wall sections are missing.
Game regularly freezes for 50-100 ms.
In the cinematic camera, the Cinema mode does not work.
When disabled interfaces, image aspect ratio is disturbed.
Goliath and Mammoth have no left life time to display.
Cuirassier, Hussaria, Light Knight, Heavy Knight, Mamluk need a barracks instead of stables to upgrade to Cavalryman.
Cirsassier, Hussaria, Light Knight do not need stables to upgrade to Red Devil.
USSR has a "Strengthened Mortars" upgrade, but no Trench mortar.
Other errors.